Integrated turbomachines are rotary machines typically including a rotating equipment housed in an outer casing, or a plurality of casings. The rotating equipment includes a shaft which is rotatingly housed in the casing(s) and which usually does not project outside the casing(s). Once the integrated turbomachine is connected to the outer piping, the inner rotating shaft is inaccessible from outside the casing(s).
Typical integrated turbomachines are comprised of a motor, such as an electric motor, and a driven turbomachine, such as a centrifugal pump or a centrifugal compressor, both housed in one or more mutually connected outer casings.
Motor-compressor units are typical examples of integrated turbomachines. These units are usually comprised of an outer casing, which houses an electric motor and a compressor, connected to one another by a driving shaft. The shaft is rotatingly supported in the casing by a plurality of bearings. In some applications, specifically in subsea applications, the casing comprises a motor compartment, which houses the electric motor, and a compressor compartment, which houses the compressor. Both compartments are sealingly closed to prevent penetration of sea water. Some subsea motor-compressor units usually employ oil-lubricated bearings for supporting the driving shaft. Recently, magnetic bearings, or active magnetic bearings have been introduced in this kind of machinery, in order to avoid certain disadvantages deriving from the presence of lubricating oil in the casing.
Other integrated turbomachines include hydrodynamic, hydrostatic or hybrid (hydrostatic/hydrodynamic) bearings, using a fluid, either liquid or gaseous, to generate a force radially or axially supporting the rotating driving shaft.
Active magnetic bearings operate without mechanical friction, but require continuous supply of electrical power. In case of lack of electrical power supply or of any other defective operation of the active magnetic bearings, the shaft needs to be supported by so-called landing bearings, sometimes named also auxiliary bearing, emergency bearings or back-up bearings. The landing bearings support the shaft when the active magnetic bearings are inoperative, e.g. for lack of electric supply.
Landing bearings provide mechanical redundancy and need to be designed and dimensioned correctly so as to prevent damages to the machine in case of failure of the active magnetic bearings. Landing bearings shall also ensure immediate recover of the machine upon removal of the cause which determined the temporary failure of the active magnetic bearings.
A landing bearing consists of a high precision mechanical bearing which can be slightly preloaded in axial and radial directions. Rolling bearings are usually used as landing or auxiliary bearings in rotary machines provided with active magnetic bearings. Typically, angular ball bearings or deep groove ball bearings mounted in pair and which may be axially preloaded, are used. These landing bearings have both axial as well as radial load capacity.
Subsea motor-compressor units are designed for operation at great depth under seawater. They are usually installed on modules which are placed on the seafloor, several hundred meters under sea level. Even though the motor-compressor module is handled with care and submerged at low speed, an impact against the seafloor cannot be avoided. This can damage the landing bearings.
Similar problems may arise in other circumstances, whenever a turbomachine is potentially subject to shocks.
Axial locking devices are known, suitable for axially locking the rotor of a turbomachine, thus preventing damages of the bearings, being these latter magnetic, hydrodynamic, hydrostatic, hybrid or rolling bearings or combination thereof. These known axial locking devices require access to the inner rotating shaft of the turbomachine and are usually placed between a shaft end and a closure member, which temporarily closes an aperture of the casing. Once the turbomachine is mounted, e.g. on a subsea module, the cover is removed and piping is fluidly connected to the interior of the casing though the aperture. The axial locking device must be removed before the turbomachine is connected to the piping. Once the axial locking device has been removed, there is no protection of the machine bearings against accidental shocks anymore.
Arrangements would thus be desirable, aimed at preventing or reducing damages to bearings, such as for instance but not exclusively landing bearings, of turbomachines, e.g. integrated turbomachines, due to shocks caused by collisions or the like.